WO 94/26999 discloses a locking system for mechanical joining of building boards, especially floorboards. A mechanical locking system permits locking together of the boards both perpendicular to and in parallel with the principal plane of the boards on long sides as well as short sides. Methods for making such floorboards are described in SE 9604484-7 and SE 9604483-9. The principles of designing and laying the floorboards as well as the methods for making the same that are described in the above three documents are applicable also to the present invention, and therefore the contents of these documents are incorporated by reference in present description.
With a view to facilitating the understanding and description of the present invention as well as the understanding of the problems behind the invention, now follows with reference to FIGS. 1-3 a brief description of floorboards according to WO 94/26999. This description of prior art should in applicable parts be considered to apply also to the following description of embodiments of the present invention.
A floorboard 1 of known design is shown from below and from above in FIGS. 3a and 3b, respectively. The board is rectangular and has a top side 2, an underside 3, two opposite long sides 4a, 4b which form joint edges, and two opposite short sides 5a, 5b which form joint edges.
Both the long sides 4a, 4b and the short sides 5a, 5b can be joined mechanically without any glue in the direction D2 in FIG. 1c. To this end, the board 1 has a planar strip 6 which is mounted at the factory and which extends horizontally from one long side 4a, the strip extending along the entire long side 4a and being made of a flexible, resilient aluminum sheet. The strip 6 can be mechanically fixed according to the illustrated embodiment, or fixed by means of glue or in some other fashion. Other strip materials can be used, such as sheet of some other metal, and aluminum or plastic sections. Alternatively, the strip 6 can be integrally formed with the board 1, for instance by some suitable working of the body of the board 1. The strip, however, is always integrated with the board 1, i.e. it is not mounted on the board 1 in connection with laying. The width of the strip 6 can be about 30 mm and its thickness about 0.5 mm. A similar, although shorter strip 6′ is arranged also along one short side 5a of the board 1. The edge side of the strip 4 facing away from the joint edge 4a is formed with a locking element 8 extending along the entire strip 6. The locking element 8 has an active locking surface 10 facing the joint edge 4a and having a height of e.g. 0.5 mm. In connection with laying, the locking element 8 cooperates with a locking groove 14, which is formed in the underside 3 of the opposite long side 4b of an adjacent board 1′. The short side strip 6′ is provided with a corresponding locking element 8′, and the opposite short side 5b has a corresponding locking groove 14′.
For mechanical joining of both long sides and short sides also in the vertical direction (direction D1 in FIG. 1c), the board 1 is further along its one long side 4a and its one short side 5a formed with a laterally open recess 16. The recess 16 is defined downwards by the associated strip 6, 6′. At the opposite edges 4b and 5b there is an upper recess 18 defining a locking tongue 20 (see FIG. 2a) cooperating with the recess 16 to form a tongue-and-groove joint.
FIGS. 1a-1c show how two such boards 1, 1′ can be joined by downwards angling. FIGS. 2a-2c show how the boards 1, 1′ can instead be joined by snap action. The long sides 4a, 4b can be joined by both methods whereas the short sides 5a, 5b—after laying of the first row—are normally joined after joining of the long sides and merely by snap action. When a new board 1′ and a previously laid board 1 are to be joined along their long sides according to FIGS. 1a-1c, the long side 4b of the new board 1′ is pressed against the long side 4a of the previously laid board 1 according to FIG. 1a, so that the locking tongue 20 is inserted into the recess 16. The board 1′ is then angled downwards to the subfloor 12 according to FIG. 1b. Now the locking tongue 20 completely enters the recess 16 while at the same time the locking element 8 of the strip 6 enters the locking groove 14. During this downwards angling, the upper part of the locking element 8 can be active and accomplish a guiding of the new board 1′ towards the previously laid board 1. In the joined state according to FIG. 1c, the boards 1, 1′ are locked in both D1 direction and D2 direction, but may be displaced relative to each other in the longitudinal direction of the joint.
FIGS. 2a-2c illustrate how also the short sides 5a and 5b of the boards 1, 1′ can be mechanically joined in both D1 and D2 direction by the new board 1′ being moved essentially horizontally towards the previously laid board 1. This can be carried out after the long side 4b of the new board 1′ has been joined as described above. In the first step in FIG. 2a, bevelled surfaces adjacent to the recess 16 and the locking tongue 20 cooperate so that the strip 6′ is forced downwards as a direct consequence of the joining of the short sides 5a, 5b. During the final joining, the strip 6′ snaps upwards as the locking element 8′ enters the locking groove 14′. By repeating the operations shown in FIGS. 1 and 2, the entire floor can be laid without glue and along all joint edges. Thus, prior-art floorboards of the above-mentioned type are joined mechanically by, as a rule, first being angled downwards on the long side, and when the long side is locked, the short sides are snapped together by horizontal displacement along the long side. The boards 1, 1′ can be taken up again in reverse order, without the joint being damaged, and be laid once more.
For optimal function, it should be possible for the boards, after being joined, along their long sides to take a position where there is a possibility of a small play between the locking surface 10 and the locking groove 14. For a more detailed description of this play, reference is made to WO 94/26999.
In addition to the disclosure of the above-mentioned patent specifications, Norske Skog Flooring AS (licensee of Valinge Aluminum AB) introduced a laminate flooring with a mechanical joining system according to WO 94/29699 in January 1996 in connection with the Domotex fair in Hannover, Germany. This laminate flooring marketed under the trademark Alloc®, is 7.6 mm thick, has a 0.6 mm aluminum strip 6 which is mechanically fixed to the tongue side and the active locking surface 10 of the locking element 8 has an inclination of about 70.degree.-80.degree. to the plane of the board. The joint edges are impregnated with wax and the underside is provided with underlay board which is mounted at the factory. The vertical joint is designed as a modified tongue-and-groove joint. The strips 6, 6′ on long side and short side are largely identical, but slightly bent upwards to different degrees on long side and short side. The inclination of the active locking surface varies between long side and short side. The distance of the locking groove 14 from the joint edge, however, is somewhat smaller on the short side than on the long side. The boards are made with a nominal play on the long side which is about 0.05-0.10 mm. This enables displacement of the long sides and bridges width tolerances of the boards. Boards of this brand have been manufactured and sold with zero play on the short sides, which is possible since the short sides need not be displaced in connection with the locking which is effected by snap action. Boards of this brand have also been made with more bevelled portions on the short side to facilitate snapping in according to FIGS. 2a-c above. It is thus known that the mechanical locking system can be designed in various ways and that long side and short side can be of different design.
WO 97/47834 (Unilin) discloses a mechanical joining system which is essentially based on the above known principles. In the corresponding product which this applicant began to market in the latter part of 1997, biasing between the boards is strived for. This leads to high friction and difficulties in angling together and displacing the boards. This document also shows that the mechanical locking on the short side can be designed in a manner different from the long side. In the described embodiments, the strip is integrated with the body of the board, i.e. made in one piece with and of the same material as the body of the board.